There are a lot of factors that go into whether or not a plebe is capable of playing football at the Naval Academy.
Plebe summer sometimes wipes out certain incoming midshipmen, causing them to lose weight or otherwise be physically weakened.
Of course, the academic and military demands of the academy are often overwhelming for a freshman. Factor in the daily rigors of football and they simply cannot handle it all.
It has been proven over the years that recruits who spend a year at the Naval Academy Prep School tend to arrive in Annapolis much more prepared to play than those that come in direct.